1. Field of the Invention
The present invention relates to a process for preparing a catalyst used in producing methacrylic acid by the gas-phase catalytic oxidation of methacrolein.
2. Description of the Prior Art
Hitherto, in producing methacrylic acid by the gas-phase catalytic oxidation of methacrolein, it has been found to be advantageous to keep the yield high by operating at a low reaction temperature from the perspective of the life of the catalysts, inhibition of side reactions, cost of equipments, etc. However, when catalysts prepared by the conventional methods are used, satisfactory results are not always obtained.
One possible reason for this is that the specific surface area dimension and the distribution of micropores of the catalyst, which are important to the oxidation reaction, have not sufficiently been controlled. In order to improve these defects, the following various trials have been made at the time of preparation of the catalyst: Addition of a carboxylic acid or polyhydric alcohol (refer to Japanese Patent Application Kokai No. 51-136615), addition of an alcohol or glycol (refer to ibid, No. 55-73347), addition of pyridine or its derivative (refer to ibid. No. 47-38591, No. 57-171444), addition of quinoline or its derivative (refer to ibid. No. 60-209258), addition of aqueous ammonia or ammonium nitrate (refer to ibid. No. 57-165040), etc. However, these methods have various defects such that, for example, the reaction results are not satisfactory; the catalytic activity is largely reduced with the lapse of time; the reaction temperature is too high; and the heat-treatment method, which is a catalyst-activating treatment, is troublesome because of the use of organic substances. The catalysts thus obtained, therefore, are not satisfactory as industrial catalysts.